The present invention relates to an electromagnetic contactor having two units of electromagnetic contactors in which an interlock mechanism provided between the two units is set in such a way that one of units is kept inoperative while the other is operating.
Electromagnetic contactors of this type are already well known. When the direction in which a motor is rotated is reversed, for example, the electromagnetic contactor is effectively employed to prevent a power source from being short-circuited in such a way that one of units for rotating the motor in a direction is closed simultaneously with the other for rotating the motor is opposite direction. One of these electromagnetic contactors which have been widely employed is shown in FIG. 1. An electromagnetic contactor unit 12 for rotating the motor in a direction and another electromagnetic contactor unit 13 for rotating the motor in opposite direction are mounted on a common base 14. Between units 12 and 13 is also mounted an interlocking device 15 on the base 14. Each of units 12 and 13 includes a fixed iron core 16, a movable iron core 17, an exciting coil 20 wound around the fixed iron core 16, a contact mechanism 21, a spring 22 for urging the movable iron core 17 upwards, and a housing 23 made of plastics and enclosing these components. Coil 20 and contact mechanism 21 are provided with electrical members such as terminals connected to an external circuit, and at least a pair of contacts are arranged in the contact mechanism 21 to be opened and closed according to the movement of movable iron core 17. However, these electrical members and contacts are omitted in FIG. 1 because they have no relation with the gist of the present invention. When coils 20 of units 12 and 13 are excited, movable iron cores 17 are drawn downwards to close pairs of contacts in contact mechanisms. The interlocking device 15 serves to prevent both contact mechanisms 21 from being closed simultaneously. The interlocking device 15 includes a bearing stand 24 erected on the base 14, and an interlocking member 26 which is fitted onto a shaft 25 attached to the bearing stand 24 and rotatable in both of clockwise and counterclockwise directions. This interlocking device 26 has arms 30a and 30b each having a same length and extending in opposite directions to project into the inside of housing 23 of units 12 and 13 through a window 27, which is provided in opposite side walls of housings 23, respectively. Each of arms 30a and 30b extends under a movable rod 31 attached to the movable iron core 17. When the unit 12 is excited and the movable iron core 17 is lowered, the pair of contacts inside are closed, the left arm 30a is pressed downwards, the interlocking member 26 is rotated in counterclockwise direction, and the right arm 30b is lifted to contact the lower end of movable rod 31 of unit 13 at the foremost end thereof, preventing the movable rod 31 from being lowered. Therefore, the pair of contacts are kept opened inside the contact mechanism 21 of unit 13 even when the unit 13 is excited. It is because iron cores 16 and 17 of unit 12 are closely contacted with each other while those of unit 13 are separated from each other and the pulling force between iron cores 16 and 17 of unit 12 is larger than that between those of unit 13 to thereby keep iron cores 16 and 17 of unit 12 not separated by the excitation of unit 13.
As described above, conventional electromagnetic contactors each having a mechanical interlock mechanism are effective in operation. However, control circuits in the field of power transmission and distribution and in various plants have become complicated these days in such a way that various electrical parts and instruments are attached to a power distribution or control board, and it has been therefore desired to make these various parts and instruments simple and small-sized. Same thing can be said about electromagnetic contactors. The inventor of the present invention reviewed conventional electromagnetic contactors with a mechanical interlock mechanism in detail and invented a structure which allows electromagnetic contactors each having a mechanical interlock mechanism to be simple and smaller-sized. When units 12 and 13 are not excited, both movable iron cores 17 are lifted by spring 22 to have a distance L from fixed iron cores 16, respectively. L is a range at which the movable iron core 17 and therefore the movable rod 31 can move, and can be called as the stroke of each of movable iron core 17 and movable rod 31. The shaft 25 of interlocking device 15 is arranged in the center between units 12 and 13 and in the center of stroke of movable rod 31. Even when the unit 12 is excited, the movable iron core 17 is lowered and the arm 30a is lowered while the arm 30b is lifted to contact the movable rod 31 of unit 13 preventing the movable rod 31 of unit 13 from being lowered, the arm 30b can not lift the movable rod 31 of unit 13 higher than the level of movable rod 31 of unit 12 unless the movable rod 31 of unit 12 is lowered by a distance larger than half the stroke thereof. Accordingly, the lowering distance which corresponds substantially to the half of stroke from the non-excited position of movable iron core 17 can be called as a play distance in interlocking operation.
The interlocking mechanism 15 of conventional electromagnetic contactor 10 has a larger play distance in the above-mentioned sense. In addition, the relatively bulky and complicated interlocking device 15 is arranged between both units thus making large the height and width of electromagnetic contactor 10. Further, assembly and adjustment of interlocking mechanism 15 are not easy. For the purpose of assembling and adjusting the interlocking device in such a way that the shaft 25 of interlocking device 15 is positioned in the center of stroke of lower end of movable rod 31, it is necessary to correctly mount the bearing stand 24, shaft 25 and interlocking member 26 on the base 14. These assembly and adjustment are not easy and take a long time because of many parts and dimension and assembly errors of related parts.